Underspecification of intents in a natural language processing system

ABSTRACT

A natural language processing system has a hierarchy of user intents related to a domain of interest, the hierarchy having specific intents corresponding to leaf nodes of the hierarchy, and more general intents corresponding to ancestor nodes of the leaf nodes. The system also has a trained understanding model that can classify natural language utterances according to user intent. When the understanding model cannot determine with sufficient confidence that a natural language utterance corresponds to one of the specific intents, the natural language processing system traverses the hierarchy of intents to find a more general user intent that is related to the most applicable specific intent of the utterance and for which there is sufficient confidence. The general intent can then be used to prompt the user with questions applicable to the general intent to obtain the missing information needed for a specific intent.

FIELD OF ART

The present invention generally relates to the field of natural languageprocessing, and more specifically, to determining user intents fromnatural language utterances.

BACKGROUND

There are many ways to provide natural language as input to a computersystem. However, such systems are not necessarily prepared to respondwith ease to utterances that are input in a natural language. If asystem were not sufficiently confident about the intent of a user, thesystem could either query a human intent analyst for clarification orpresent the user with a long list of possible intents. Human analystsare skilled at quickly determining user intents, but it is costly toemploy teams of analysts to provide clarification to computer systems inreal time. An alternative—responding to the user with a long list ofpossible options—can frustrate the user by becoming repetitive and bymaking it seem as though the system completely failed to understand theuser input.

SUMMARY

A natural language processing system interprets natural language inputs(hereinafter “utterances”) of users and, in cases where it cannotdetermine the users' most specific intents, leverages the informationthat it does understand to determine more general intents and to respondwith intelligent prompts and questions related to the general intents todetermine more specific intents.

For each domain of interest that a particular company or otherorganization might have there is an intent ontology (hereinafter “domainhierarchy”). The various domain hierarchies may either be separate, orthey may be combined into a single hierarchy that encompasses them all.The intents associated with the leaf nodes of a domain hierarchyrepresent specific user intents. For example, a specific intent of auser may be to “Book a flight.” Ideally, the system recognizes this userintent based on a given utterance. However, for a given utterance, ifthe system cannot classify the utterance as corresponding to a specificintent with a confidence that exceeds some minimum threshold ofconfidence, then the system determines confidence scores for non-leaf(also referred to as “ancestor”) nodes in the domain hierarchy, whichrepresent more general intents. The nodes that the system evaluates withrespect to the utterance are the ancestor nodes of the leaf nodes thatrepresent user intents that the system most confidently associates withthe utterance. An ancestor node is selected when the system issufficiently confident that the ancestor node intent is the same as theintent specified by the utterance.

Although the ancestor node represents a general intent that is lessspecific than that of the leaf node, the system is still able to gaininformation about what the user wants. For example, the system mayunderstand that a user has the general intent “Booking,” even if itcannot understand that the user specifically wants to book a flight.With the information it was able to gain from the general intent, thesystem can intelligently prompt the user for more specific informationabout the user intent, without needing to rely on a top-level menu ofgeneric options or on a human intent analyst to determine the user'smeaning.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the inventive subject matter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a high-level block diagram of a computing environmentin which users interact with a computer system using natural language,according to one embodiment.

FIG. 2 is a high-level block diagram illustrating a detailed view of thenatural language processing system from FIG. 1, according to oneembodiment.

FIG. 3A is a sample domain hierarchy of intents, according to oneembodiment.

FIG. 3B is the sample domain hierarchy of intents of FIG. 3A with sampleconfidence scores, according to one embodiment.

FIG. 4 is a high-level block diagram illustrating physical components ofa computer used as part or all of the computing environment from FIG. 1,according to one embodiment.

The figures depict embodiments of the present invention for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles of the invention described herein.

DETAILED DESCRIPTION System Environment

FIG. 1 illustrates a high-level block diagram of a computing environmentin which users interact with a computer system using natural language,according to one embodiment. A client device 120 communicates userutterances over a network 140. A natural language processing system 100,being also connected to the network 140, provides natural languageinterpretation services on behalf of a merchant system 110. Based on itsinterpretation of user utterances, the natural language processingsystem 100 can determine an appropriate response to send to the user andcan provide rational feedback to the user via the client device 120. Inone embodiment, the natural language processing system 100 providesinterpretations of user utterances to the merchant system 110, which canthen determine a response to deliver to the client device 120. Thesevarious components are now described in additional detail.

Upon receipt of an utterance, the natural language processing system 100determines an intent represented by that utterance. The natural languageprocessing system 100 will be described in more detail with respect toFIG. 2.

The client device 120 is a computing device such as a smart phone,laptop computer, desktop computer, or any other device that can receiveuser utterances in a natural language form, such as text or voice input.The client device 120 communicates the utterance over the network 140 tothe natural language processing system 100, where the utterance isinterpreted.

The network 140 may be any suitable communications network for datatransmission. In an embodiment such as that illustrated in FIG. 1, thenetwork 140 uses standard communications technologies and/or protocolsand can include the Internet. In another embodiment, the entities usecustom and/or dedicated data communications technologies.

System Architecture

FIG. 2 is a high-level block diagram illustrating a detailed view of thenatural language processing system 100 from FIG. 1, according to oneembodiment. The natural language processing system 100 comprises arepository of domain hierarchies 205, a repository of intentunderstanding models 210, a repository of hierarchy understanding models240, a repository of dialogue scripts 230, an utterance response module235, and an intent determination module 220. In one embodiment, theintent determination module 220 in turn comprises a hierarchydetermination module 221, and a node scoring module 222. In oneembodiment, the natural language processing system 100 further comprisesa repository of task models and a repository of user models (notillustrated in FIG. 2).

The dialogue scripts 230 comprise words, phrases, or other prompts forresponding to the user utterances (e.g., to the intents determined forthe user utterances). According to one embodiment, a dialogue script canalso reference certain task models and user models. For example, adialogue script can contain a variety of words, phrases and prompts thatthe utterance response module 235 uses to respond to a user intent. Theparticular response that the utterance response module 235 uses torespond to a user utterance may depend on the task stored in therepository of task models that is related to the intent and a user modelfrom the repository of user models that may determine which responsewill be best suited to the particular user. As one example, if thedetermined user intent for an utterance were to book a flight, thedialogue scripts 230 might contain the response “OK, it sounds likeyou'd like to book a flight. Please say the city from which you'd liketo depart.” In some embodiments, the specific content of the response(corresponding to the data to be obtained) is determined by the taskmodels.

The task models comprise information about what processes must takeplace to complete certain tasks. The task models may further compriseinformation about what data must be obtained from the user, or fromother sources, to accomplish the tasks. For example, a task model forbooking a flight could comprise asking for the destination city andtraveling days, determining whether any flights are available on thetraveling days, and obtaining the passenger's name, seat preference, andcredit card number. Based on a task model, the system determines thebest way to prompt a user for the information that is relevant to thespecific task.

The user models comprise information about the kind of users that areproviding user utterances to the client device 120. For example, in someembodiments, the system can recognize a user based on an identifier suchas the telephone number of the phone that the user calls from to accessthe system. In some cases, such as for a returning user, the system mayhave voice recognition models trained to understand the user's voice.This information is stored as part of a user model that the intentdetermination module 220 can use to better understand the user'smeaning. The user models may also contain user-specific preferences,such as prompts that are chosen for that specific user to enhancerelevance or understandability for that user.

Domain hierarchies, stored within the repository of domain hierarchies205, are hierarchical graphs having leaf nodes and non-leaf nodes(hereinafter referred to as “ancestor nodes” of the leaf nodes, in thatthey may be parents of leaf nodes, parents of parents, etc.). Each noderepresents a possible user intent. Each leaf node represents a differentspecific user intent (the most specific that the domain hierarchy inquestion recognizes), and the ancestor nodes represent related but moregeneral user intents.

For example, FIG. 3A is a sample domain hierarchy of intents, accordingto one embodiment. The example of FIG. 3A is a domain hierarchyconstructed to represent airline services. It comprises ancestor nodes360 that represent general user intents. According to this exampledomain hierarchy, one ancestor node represents a general user intent of“Booking”. The example domain hierarchy of FIG. 3A further comprisesleaf nodes 370 that represent specific user intents such as “Check in”,“Book a flight”, “Book a rental car”, “Book a hotel room”, and “Checkflight status.” Some of the leaf nodes 370 are descendants of theancestor node 360 that represents the general user intent of “Booking”because the specific intents to “Book a flight”, “Book a rental car”,and “Book a hotel room” are all more specific versions of that generalintent. According to the embodiment shown in FIG. 3A, the domainhierarchy also has an ancestor node that is the root node of the domainhierarchy. That is, it is the ancestor node 360 of the domain hierarchyfrom which all other nodes in the hierarchy are descended. According toone embodiment, the root node represents the most general, i.e. leastspecific, user intent.

Returning again to FIG. 2, the hierarchy understanding models 240include a model for each domain hierarchy 205. Hierarchy understandingmodels 240 map basic information about user utterances to one or moredomain hierarchies 205 that are likely to contain information applicableto the user's specific intent. The hierarchy determination module 221uses the models 240 when determining which of the domain hierarchies 205is most applicable for a given utterance and hence should be analyzedwith respect to the utterance; in some embodiments, each of thehierarchy understanding models 240 is applied to the given utterance,and a most applicable domain hierarchy 205 is selected based on theresults (e.g., the domain hierarchy 205 whose corresponding hierarchyunderstanding model 240 produces the highest score for the utterance).In one embodiment, a hierarchy understanding model 240 is trained usingsupervised machine learning, in which a training set upon which thehierarchy understanding model is trained contains utterances that arelabeled with the general user intents they are known to represent. Inone embodiment, the hierarchy understanding model 240 is trained usingmultinomial logistic regression. Other training techniques may beemployed in other embodiments, such as support vector machines, deepneural networks, naïve Bayes, and decision trees.

The intent understanding models 210 comprise an understanding model foreach intent node in a domain hierarchy 205. (As a specific examplepurely for the purposes of illustration, one sample 4-node domainhierarchy 205A is illustrated in FIG. 2, each node depicted with acircle and its corresponding intent understanding model depicted with asquare.) An understanding model for a given intent node takes anutterance as input and produces as output a confidence score indicatingwhether the utterance represents the intent corresponding to the intentnode, e.g., as a scalar value representing a probability value, or thelike.

In one embodiment, the intent understanding model for each intent nodeis trained using supervised machine learning, in which a training setupon which the intent understanding model is trained contains utterancesthat are labeled with the user intents the utterances are known torepresent. In one embodiment, the intent understanding models 210 aretrained using multinomial logistic regression. Other training techniquessuch as support vector machines, deep neural networks, naïve Bayes, anddecision trees may be employed in other embodiments.

The intent determination module 220 associates a user utterance with anoutput comprising an intent and a confidence score associated with theintent. For example, if the user utterance were “I would like to book aflight”, the output of the intent determination module 220 might be<BookFlight, 0.85>, indicating the “Book Flight” intent with aconfidence score of 0.85. In one embodiment, the intent determinationmodule 220 comprises the hierarchy determination module 221, and thenode scoring module 222.

For a given utterance, the hierarchy determination module 221 determineswhich domain hierarchies 205 should be used to determine a user'sspecific intent. The hierarchy determination module 221 applieshierarchy understanding models 240 to the user utterance. In oneembodiment, each hierarchy understanding model outputs a score (e.g., areal number value) indicating a likelihood that the domain hierarchy towhich the model corresponds contains information that is applicable to ageneral intent of the user (and should therefore be used to determinethe more specific intent of the user). The hierarchy determinationmodule 221 selects a subset of one or more of the applicable domainhierarchies for the intent determination module 220 to use to determinea specific user intent. For example, the hierarchy determination modelmight select a domain hierarchy of actions related to purchasingproducts (e.g., buy, return, refund) and a domain hierarchy of products(e.g., ticket, car, gift card).

For a given subset of domain hierarchies and a given utterance, the nodescoring module 222 determines a confidence score for some or all of theintents in the one or more domain hierarchies 205 that were selected bythe hierarchy determination module 221. The node scoring moduledetermines confidence scores for leaf nodes by applying the intentunderstanding models 210 corresponding to nodes in the one or moredomain hierarchies.

Once the intent determination module 220 has identified a node whoseconfidence score exceeds the minimum confidence threshold for a givenutterance, the intent determination module 220 outputs an identificationof the intent associated with a chosen node and (optionally) theconfidence score associated with the chosen node. In embodiments inwhich multiple domain hierarchies are used to determine an intent, theintent determination module 220 outputs information about nodes that arechosen from each of the domain hierarchies (e.g., in the form of a listof the portions of the overall intent) if each node exceeds the minimumconfidence threshold.

The natural language processing system 100 further comprises anutterance response module 235 that uses the intent determined by theintent determination module 220 to respond to the user. Depending on theuser intent, the utterance response module 235 accesses a dialoguescript from a dialogue script repository 230 which contains informationabout how to respond to the intent, such as prompts, phrases, or otherresponses to make to the user. In some embodiments, the utteranceresponse module 235 also accesses task models and user models based onthe user intent. In cases where a general, rather than specific, intentwas chosen by the intent determination module 220 (i.e. an ancestor nodewas selected instead of a leaf node), the dialogue scripts 230 caninclude prompts for clarification about the specific intent of the user.For example, if the intent determination module 220 determines that auser has a general intent of “Booking,” then a dialogue script mightcontain instructions for giving the user the prompt “I see that you areinterested in booking. Would you like to book a flight, book a hotelroom, or book a rental car?” In this way, the system can provide usefulprompts that ask for specific clarifications (e.g., what specific typeof thing to book), instead of frustrating a user by asking a the mostgeneral question about user intent (e.g., “I didn't get that; please sayit again”). In one embodiment, the utterance response module 235 and thedialogue script repository 230 (along with the task models and the usermodels) are hosted by the merchant system 110 instead of by the languageprocessing system 100.

Under-Specification Algorithms

The scores produced by the node scoring module 222 are used by theintent determination module 220 to determine a most likely specificintent that corresponds to a user utterance. Various ways of determininguser intents using confidence scores are now described.

In one embodiment, the node scoring module 222 scores every node in eachof the domain hierarchies selected by the hierarchy determination module221. If the confidence score associated with at least one of theseintents exceeds a minimum confidence threshold, then an output isproduced by the natural language processing system 100 comprising theintent with the highest confidence score and (in some embodiments) theconfidence score associated with the intent.

If the intent determination module 220 determines that none of thedetermined confidence scores exceeds the minimum confidence threshold,the intent determination module 220 tries to identify an ancestornode(s) that represents an intent that most closely corresponds to thegiven user utterance. The intent determination module 220 examines therelationship between the two nodes corresponding to the two intents withthe two highest confidence scores. If the two nodes have a parent childrelationship as expressed in their corresponding intent hierarchy, thenthe intent determination module outputs the parent node, i.e. the moregeneral node. In a situation in which the nodes of multiple domainhierarchies are scored, this procedure is applied to each hierarchy, andthe final output is the concatenation of the results from eachhierarchy. For example, there may be two domain hierarchiescorresponding to verbs and nouns, respectively. In one particularexample, the output of the intent determination module 220 might be<book, flight> with a confidence score of 0.25. If this score is lessthan the minimum confidence threshold, then the intent determinationmodule 220 may ascertain from the two highest scoring verb intents that<book> should still be output, and conversely determine from the twohighest scoring noun intents that <Root> should be output. Consequently,the intent determination module 220 would output <book, Root> as theintent (i.e., the user wants to complete a booking of some kind).

In other embodiments, the confidence scores of only the leaf nodes in aparticular hierarchy are computed first. If none of the leaf nodesreceive scores of sufficient confidence, then the trained intentunderstanding models 210 of all or some of the ancestor nodesimmediately connected to the leaf nodes are evaluated with respect tothe given utterance. This process is repeated, evaluating the next setof nodes up in the hierarchy until either a node is determined to have ascore of sufficient confidence, or a root node of the hierarchy isreached, indicating that the utterance does not match any of thepossible user intents, even the general intents. It is appreciated thatin one embodiment, the intent understanding models 210 of all ancestornodes between a leaf node and the root node are used to evaluate theutterance before the ancestor nodes of other leaf nodes are evaluatedand assigned scores and typically without reevaluating an ancestor nodethat was scored previously.

According to some embodiments, the confidence score of an ancestor nodeis determined based on the scores of other nodes, such as the leaf nodesor other ancestor nodes. Examples of algorithms that can be used toscore ancestor nodes include: using the geometric mean of the scores ofdescendant nodes to compute the score for their ancestor node, computingthe maximum score of the descendant nodes, or directly identifying thescore of the ancestor node without aggregating from the descendantnodes. The particular way in which the scores are determined differs indifferent embodiments, some of which are subsequently detailed.

In one embodiment, if no leaf nodes receive adequately high confidencescores, then the scores of ancestor nodes are determined using thearithmetic mean of the corresponding leaf nodes. That is, for some orall ancestor nodes that are immediately adjacent to at least one leafnode, the average value of the confidence scores of all leaf nodes thatare descendants of the ancestor node in question is determined andassigned as the confidence score of that ancestor node. In someembodiments, the confidence scores of ancestor nodes are determinedusing the geometric mean, rather than the arithmetic mean, in which casethe descendant leaf node scores are multiplied together then the nthroot of the result is taken, where n is the number of descendant leafnodes. The confidence score of the ancestor node is then compared to anew threshold value, lower than the initial threshold value used for theleaf node confidence scores, and tested against that new threshold valueto determine whether the confidence score for the ancestor node is highenough for the ancestor node to be chosen as representing the userintent. (As an alternative to choosing a new, lower threshold value, theconfidence scores of the ancestor nodes may be increased, e.g., by amultiplier, and compared to the initial threshold value.) If theconfidence score of the ancestor node is not sufficiently great, theprocess is repeated (i.e. scoring the ancestor nodes adjacent to thepreviously scored nodes), until a node of significantly high confidenceis chosen or the root of the hierarchical structure is reached.

For example, FIG. 3B shows one possible embodiment of determining a userintent for a domain hierarchy for an airline, where the confidencescores of ancestor nodes are computed using an arithmetic mean. The leafnodes 370, which represent specific user intents, have accompanyingconfidence scores assigned by the node scoring module 222 in response toan utterance. In the example embodiment of FIG. 3B, confidence scoresare values between 0 and 100, where a score of 100 for an intentindicates the highest possible confidence that the utterance correspondsto that intent, and a score of 0 indicates the lowest possibleconfidence that the utterance corresponds to that intent. It isappreciated that confidence scores may be presented in different ways,or with different ranges, in other embodiments. For the purposes of theexample, a minimum sufficient confidence score 380 has a value of 80.Since none of the leaf nodes shown in FIG. 3B received confidence scoresof at least 80, a confidence score is determined for those ancestornodes that are immediately adjacent to a leaf node. The “Booking” intenthas three descendants that are leaf nodes: “Book a flight” with a scoreof 77, “Book a rental car” with a score of 67, and “Book a hotel room”with a score of 48. Accordingly, the ancestor node representing the“Booking” intent receives a score of 64, which is the arithmetic mean ofthe scores of those three leaf node descendants. If, in the example ofFIG. 3B, there were an additional ancestor node from which the“Booking”, “Check-in”, and “Check flight status” nodes descended, thatnode would receive a confidence score based on the arithmetic mean ofall leaf nodes that are descended from it. Namely, its leaf nodedescendants would include “Check in” with a score of 11, “Book a flight”with a score of 77, “Book a rental car” with a score of 67, “Book ahotel room” with a score of 48, and “Check flight status” with a scoreof 52, and it would thus receive a score of 51, the average of theconfidence scores of the leaf nodes. In this example, assume that thenew threshold value were reduced to 80% of the prior threshold (of 70,in this example). Thus, the threshold confidence score value becomes 56.The newly scored nodes are examined, and it is found that “Booking” witha score of 64 exceeds this new confidence score threshold. As a result,“Booking” is chosen as a general intent that corresponds to theutterance.

According to one embodiment, if no leaf nodes receive confidence scoreshigher than the confidence threshold, a collection of all leaf nodeswith scores higher than some predetermined value is found. The nearestcommon ancestor node to all the nodes in the group of chosen nodes isidentified as a general intent of the user. It is appreciated that thistechnique may also be used by other confidence score determinationmethods in other embodiments as one possible way to break a tie in thecase that two nodes receive identical confidence scores.

For example, the technique of using nearest common ancestor nodes tochoose a general intent that corresponds to the utterance is describedwith respect to the sample domain hierarchy of FIG. 3B. An exampleminimum confidence score 380 is established with a value of 80. For thesake of the example, a predetermined value of 60 is established as acutoff value for determining which leaf node confidence scores 390 willbe considered when finding a nearest common ancestor. Since none of theexample confidence scores 390 that are assigned to the leaf nodes isgreater than or equal to 80, the example minimum sufficient confidence380, the leaf nodes with confidence scores greater than or equal to 60are found. In this example, these leaf nodes represent the intent “Booka flight” with a score of 77, and the intent “Book a rental car” with ascore of 67. The nearest common ancestor node of both the intent to“Book a flight” and the intent to “Book a rental car” is the node thatrepresents the intent “Booking”. As a result, “Booking” is chosen as ageneral intent that corresponds to the utterance.

In one embodiment, if none of the leaf nodes receive sufficiently highconfidence scores, some or all ancestor nodes that are adjacent to atleast one leaf node receive scores equal to the maximum value of thescores received by some or all leaf nodes that are descendants of theancestor node in question. In some cases, the minimum value of scoresreceived by some or all leaf nodes that are descendants of the ancestornode may be used to determine the new scores, rather than the maximumvalue. In some embodiments, the new scores are incremented by somepredetermined amount; in other embodiments, the minimum confidencethreshold is decreased by some predetermined amount. The newly scorednodes are then compared against the minimum confidence threshold. Theprocess is repeated, propagating up the hierarchy, until a node receivesa score that is at least as high as the value of the thresholdconfidence value, or until the node at the root of the domain hierarchyis reached.

For example, the technique of using maximum values of descendant leafnodes to determine scores for ancestor nodes is shown with respect tothe sample domain hierarchy in FIG. 3B. Since all of the leaf nodes inFIG. 3B received confidence scores 390 with values less than 80, theminimum sufficient confidence score 380, those ancestor nodes adjacentto leaf nodes are scored. The ancestor node that represents the intent“Booking” has three descendant leaf nodes: “Book a flight” with a scoreof 77, “Book a rental car” with a score of 67, and “Book a hotel room”with a score of 48. The “Booking” ancestor node is assigned a score of77, the maximum value of the three descendant leaf node scores. The rootnode is another ancestor node which is adjacent to at least one leafnode. The root node has five descendant leaf nodes. They are “Check in”with a score of 11, “Book a flight” with a score of 77, “Book a rentalcar” with a score of 67, “Book a hotel room” with a score of 48, and“Check flight status” with a score of 52. The root node receives aconfidence score of 77, the maximum of the five descendant leaf nodescores. For the sake of this example, the example minimum sufficientconfidence value 380 is decreased by a predetermined amount of 20. Thus,the newly scored nodes are compared to a new minimum sufficientconfidence score value of 60. Both newly scored nodes have scores of 77,so both have scores that exceed the cutoff value of 60. Thus either theintent “Booking” or the root node are chosen to represent the utterance,according to some predetermined tie-breaking procedure such asdetermining the nearest common ancestor node of both nodes.

According to one embodiment, two domain hierarchies from the repositoryof domain hierarchies 205 are used to classify user intents. The userintent is divided into a <verb, noun> pair, with one intentunderstanding model 210 corresponding to the “verb” part and anotherintent understanding model 210 corresponding to the “noun” part. Theverb refers to a node in a domain hierarchy that contains user intentsrelated to actions. The noun refers to a node in another domainhierarchy that contains user intents related to objects that are to beacted on. For example, in such an embodiment, if the user wants to askan airline for information about a flight status, the verb could be“check” and the noun could be “flight status”. The node scoring module222 determines a confidence score for a <verb, noun> pair by combiningthe intent understanding models 210 associated with the verb and thenoun, respectively. The node scoring module 222 obtains a confidencescore for the <verb, noun> pair by defining a function that takes asinput the verb confidence score and the noun confidence score andoutputs a new confidence score for the <verb, noun> pair. An example ofa function for combining a verb confidence score and a noun confidencescore is a minimum function. For example, if a <verb, noun> pair is<book, flight>, the intent understanding model associated with the verbnode might assign a confidence score of 0.95 to the verb “book” whilethe intent understanding model associated with the noun node mightassign 0.85 to the noun “flight”. Consequently, the minimum functionwould assign the confidence score 0.85 to the pair <book, flight>because 0.85 is less than 0.95. Computer System Components

FIG. 4 is a high-level block diagram illustrating physical components ofa computer 400 used as part or all of the computing environment fromFIG. 1, according to one embodiment. Illustrated are at least oneprocessor 402 coupled to a chipset 404. Also coupled to the chipset 404are a memory 406, a storage device 408, a graphics adapter 412, and anetwork adapter 416. A display 418 is coupled to the graphics adapter412. In one embodiment, the functionality of the chipset 404 is providedby a memory controller hub 420 and an I/O controller hub 422. In anotherembodiment, the memory 406 is coupled directly to the processor 402instead of the chipset 404.

The storage device 408 is any non-transitory computer-readable storagemedium, such as a hard drive, compact disk read-only memory (CD-ROM),DVD, or a solid-state memory device. The memory 406 holds instructionsand data used by the processor 402. The graphics adapter 412 displaysimages and other information on the display 418. The network adapter 416couples the computer 400 to a local or wide area network.

As is known in the art, a computer 400 can have different and/or othercomponents than those shown in FIG. 4. In addition, the computer 400 canlack certain illustrated components. In one embodiment, a computer 400acting as a server may lack a graphics adapter 412, and/or display 418,as well as a keyboard or pointing device. Moreover, the storage device408 can be local and/or remote from the computer 400 (such as embodiedwithin a storage area network (SAN)).

As is known in the art, the computer 400 is adapted to execute computerprogram modules for providing functionality described herein. As usedherein, the term “module” refers to computer program logic utilized toprovide the specified functionality. Thus, a module can be implementedin hardware, firmware, and/or software. In one embodiment, programmodules are stored on the storage device 408, loaded into the memory406, and executed by the processor 402.

Embodiments of the entities described herein can include other and/ordifferent modules than the ones described here. In addition, thefunctionality attributed to the modules can be performed by other ordifferent modules in other embodiments. Moreover, this descriptionoccasionally omits the term “module” for purposes of clarity andconvenience.

Other Considerations

The present invention has been described in particular detail withrespect to one possible embodiment. Those of skill in the art willappreciate that the invention may be practiced in other embodiments.First, the particular naming of the components and variables,capitalization of terms, the attributes, data structures, or any otherprogramming or structural aspect is not mandatory or significant, andthe mechanisms that implement the invention or its features may havedifferent names, formats, or protocols. Also, the particular division offunctionality between the various system components described herein ismerely for purposes of example, and is not mandatory; functionsperformed by a single system component may instead be performed bymultiple components, and functions performed by multiple components mayinstead performed by a single component.

Some portions of above description present the features of the presentinvention in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. These operations, while describedfunctionally or logically, are understood to be implemented by computerprograms. Furthermore, it has also proven convenient at times, to referto these arrangements of operations as modules or by functional names,without loss of generality.

Unless specifically stated otherwise as apparent from the abovediscussion, it is appreciated that throughout the description,discussions utilizing terms such as “determining” or “displaying” or thelike, refer to the action and processes of a computer system, or similarelectronic computing device, that manipulates and transforms datarepresented as physical (electronic) quantities within the computersystem memories or registers or other such information storage,transmission or display devices.

Certain aspects of the present invention include process steps andinstructions described herein in the form of an algorithm. It should benoted that the process steps and instructions of the present inventioncould be embodied in software, firmware or hardware, and when embodiedin software, could be downloaded to reside on and be operated fromdifferent platforms used by real time network operating systems.

The present invention also relates to an apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored on acomputer readable medium that can be accessed by the computer. Such acomputer program may be stored in a non-transitory computer readablestorage medium, such as, but is not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, magnetic-optical disks,read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, application specific integratedcircuits (ASICs), or any type of computer-readable storage mediumsuitable for storing electronic instructions, and each coupled to acomputer system bus. Furthermore, the computers referred to in thespecification may include a single processor or may be architecturesemploying multiple processor designs for increased computing capability.

The algorithms and operations presented herein are not inherentlyrelated to any particular computer or other apparatus. Variousgeneral-purpose systems may also be used with programs in accordancewith the teachings herein, or it may prove convenient to construct morespecialized apparatus to perform the required method steps. The requiredstructure for a variety of these systems will be apparent to those ofskill in the art, along with equivalent variations. In addition, thepresent invention is not described with reference to any particularprogramming language. It is appreciated that a variety of programminglanguages may be used to implement the teachings of the presentinvention as described herein, and any references to specific languagesare provided for invention of enablement and best mode of the presentinvention.

The present invention is well suited to a wide variety of computernetwork systems over numerous topologies. Within this field, theconfiguration and management of large networks comprise storage devicesand computers that are communicatively coupled to dissimilar computersand storage devices over a network, such as the Internet.

Finally, it should be noted that the language used in the specificationhas been principally selected for readability and instructionalpurposes, and may not have been selected to delineate or circumscribethe inventive subject matter. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting, of the scopeof the invention, which is set forth in the following claims.

1. A non-transitory computer-readable storage medium comprisinginstructions executable by a processor, the instructions comprising:instructions for receiving a natural language utterance specified by auser; instructions for accessing a domain hierarchy of intentscomprising leaf nodes and ancestor nodes, wherein each of a plurality ofthe leaf nodes has a corresponding intent understanding model trainedthrough supervised machine learning based on respective training sets ofutterances that are labeled with user intents that the sets ofutterances are known to represent; instructions for applying a pluralityof intent understanding models of the leaf nodes to the natural languageutterance, thereby producing a corresponding plurality of leaf nodeconfidence scores; instructions for determining that none of the leafnode confidence scores exceeds a given minimum confidence threshold;instructions for, responsive to the determining, determining ancestornode confidence scores for the ancestor nodes; instructions foridentifying a most applicable ancestor node based on the ancestor nodeconfidence scores; and instructions for identifying, as a general intentof the natural language utterance, an intent corresponding to theidentified most applicable ancestor node.
 2. The non-transitorycomputer-readable storage medium of claim 1, the instructions furthercomprising: instructions for identifying, based on the identifiedgeneral intent, a prompt for additional information; and instructionsfor providing the prompt to the user over the computer network.
 3. Thenon-transitory computer-readable storage medium of claim 1, wherein anydescendant node in the hierarchy of intents corresponds to a morespecific user intent than the intents corresponding to any ancestornodes from which the descendant node is descended.
 4. The non-transitorycomputer-readable storage medium of claim 1, wherein applying the intentunderstanding models comprises associating the natural languageutterance with a verb from a domain hierarchy of actions and with a nounfrom a domain hierarchy of intents related to items.
 5. Thenon-transitory computer-readable storage medium of claim 1, whereinapplying the intent understanding models comprises associating thenatural language utterance with two or more intents, each intentselected from its own intent hierarchy.
 6. The non-transitorycomputer-readable storage medium of claim 1, wherein the ancestor nodeconfidence score is determined by calculating a function of theconfidence scores of other nodes in the same intent hierarchy.
 7. Thenon-transitory computer-readable storage medium of claim 6, wherein theancestor node confidence score is determined by calculating a geometricmean of the leaf node confidence scores of leaf nodes descended from theancestor node.
 8. The non-transitory computer-readable storage medium ofclaim 6, wherein the ancestor node confidence score is determined bydetermining a maximum confidence score of leaf nodes descended from theancestor node.
 9. The non-transitory computer-readable storage medium ofclaim 6, wherein the ancestor node confidence score is determined by:identifying an intent understanding model corresponding to the ancestornode; and applying the identified intent understanding model to thenatural language utterance.
 10. A computer-implemented methodcomprising: receiving a natural language utterance specified by a userover a computer network; accessing a domain hierarchy of intentscomprising leaf nodes and ancestor nodes, wherein each of a plurality ofthe leaf nodes has a corresponding intent understanding model trainedthrough supervised machine learning based on respective training sets ofutterances that are labeled with user intents the sets of utterances areknown to represent; applying the intent understanding modelscorresponding to each of the plurality of leaf nodes to the naturallanguage utterance, thereby producing a corresponding plurality of leafnode confidence scores; determining that none of the leaf nodeconfidence scores exceeds a given minimum confidence threshold;responsive to the determining, determining ancestor node confidencescores for the ancestor nodes; identifying a most applicable ancestornode based on the ancestor node confidence scores; and identifying, as ageneral intent of the natural language utterance, an intentcorresponding to the identified most applicable ancestor node.
 11. Thecomputer-implemented method of claim 10, further comprising:identifying, based on the identified general intent, a prompt foradditional information; and providing the prompt to the user over thecomputer network.
 12. The computer-implemented method of claim 10,wherein the leaf nodes in the hierarchy of intents correspond to morespecific user intents than the intents corresponding to the ancestornodes from which the leaf nodes are descended.
 13. Thecomputer-implemented method of claim 10, wherein applying the intentunderstanding models comprises associating the natural languageutterance with a verb from a domain hierarchy of actions and with a nounfrom a domain hierarchy of intents related to items.
 14. Thecomputer-implemented method of claim 10, wherein applying the intentunderstanding models comprises associating the natural languageutterance with two or more intents, each intent selected from its ownintent hierarchy.
 15. The computer-implemented method of claim 10,wherein the ancestor node confidence score is determined by calculatinga function of the confidence scores of other nodes in the same intenthierarchy.
 16. The computer-implemented method of claim 15, wherein theancestor node confidence score is determined by calculating a geometricmean of the leaf node confidence scores of leaf nodes descended from theancestor node.
 17. The computer-implemented method of claim 15, whereinthe ancestor node confidence score is determined by: identifying anintent understanding model corresponding to the ancestor node; andapplying the identified intent understanding model to the naturallanguage utterance.
 18. The computer-implemented method of claim 15,further comprising: applying, to the utterance, a plurality of hierarchyunderstanding models for a corresponding plurality of domain hierarchiesto produce a corresponding plurality of scores for the utterance;selecting a subset of the domain hierarchies based on the scores; andidentifying the most applicable ancestor node based on the selectedsubset.